I use Sikiflex - apllies with one of those sealant guns its available usually from auto paint supply specialists. They do colour too. Although flexible once applied importantly its not like a mastic, more like plastic - it takes about half an hour to 'cure' and drys thoroughly (unlike mastic or caulking). Applied carefully to door cards it can be invisible. You'll need to use a sharp knife to remove the trim though. I've used it in its own to secure bits of trim,